A high school production of Sweeney Todd in New Zealand went horribly wrong when a throat-slitting scene became all too real and two teenagers were sliced with a prop razor.

Students at Saint Kentigern College in Auckland were performing the opening night of the musical when the mishap happened.

Headteacher Steve Cole told radio station Newstalk ZB the razor used on stage was real, but had been bound in duct tape.

He said he had no idea what went wrong.

“It had been bound in Cellophane, bound in all sorts of things,” he said.

'Sweeney Todd: The Demon Barber Of Fleet Street' film - 2007

Johnny Depp in the 2007 film version of the musical

“It was very non-sharp, blunted, and had been through all sorts of health and safety checks. It was a very unfortunate mishap.”

The two 16-year-olds were rushed to hospital for treatment – one with serious, and the other with moderate injuries. They were released the next day and are said to be recovering.

Mr Cole said he hoped the show would resume on Friday, “obviously without those particular props”.

Sweeney Todd: The Demon Barber of Fleet Street, depicts a barber who slits his customers’ throats with a razor and uses the bodies to make meat pies.

Wednesday’s incident is being investigated by police and health and safety officials.